The present invention relates to methods and apparatus which may assist in diagnosing disorders of the musculoskeletal system and in particular the spine.
Joints of the human body permit movement through the contraction of muscular tissues acting on osseous structures (bones) which in turn are united by soft tissue linkages (ligaments). Imbalance in the relation between the rigidity and flexibility of a human joint has long been hypothesized to result in pathology and/or pain. Specifically, many musculoskeletal conditions such as hypermobility or osteoarthritis are thought to be characterized by excessive or insufficient displacements of osseous structures. While the relation between aberrant osseous motion and pathology/pain is plausible, the invasive and sometimes harmful nature of many investigative techniques has left the clinical significance of this relation incompletely understood.
Approaches which use extracted human tissues (in vitro) have described aberrant spinal kinematics in a number of pathological processes including disc degeneration1,2. While important, the clinical significance of these studies cannot be ascertained due to limitations of the in vitro process which include tissue loss, lack of tissue function and the inability to assess subjective phenomena (e.g. pain).
To resolve these limitations and address the issue of clinical significance, many investigative techniques have been employed that assess displacement of osseous structures in living humans. While use of existing in vivo techniques resolves several of these limitations, the majority are invasive and/or have the potential for harm which preclude their use in large populations. These techniques include surgical fixation3,4 and two-dimensional radiographic imaging involving ionizing radiation5-7.
For this reason, a limited number of in vivo techniques have been developed which are non-invasive8-11. Unfortunately, these techniques are considered to be highly variable due to (1) their dependency on instrumentation which attempts to relate skin movement with the displacements of underlying osseous structures and (2) their dependency on subject-generated movement to create the displacements they attempt to quantify. As a result, these non-invasive, in vivo techniques are incapable of direct quantification of spinal mechanics and/or performing controlled loading protocols.
Therefore, there is a need in the art for non-invasive methods and systems for diagnosing musculoskeletal disorders by measuring osseous displacement in response to a controlled load.
As a response to this need, the applicant has developed non-invasive methods and apparatuses that permit direct quantification of the displacement of a specific osseous structure in response to a pre-defined, externally applied load. This method, referred to herein as ultrasonic indentation (UI), is based on the principle that under an applied load, the displacement of a rigid target within a compressible medium can be determined by subtracting the resulting compression between the loading interface and the rigid target from the distance through which the load was applied (d=Aaxe2x88x92Ast, where d is the displacement of the rigid target, Aa is the displacement of the object used to apply the indentation load and Ast is the compression of the soft tissue between the interface of the indentation object and the indentation target).
In UI, an indentation load is applied to the external surface of the body by an ultrasonic transducer which is pressed bluntly into the soft tissues overlying the bone of interest either by hand or by mechanical actuation. The displacement of the ultrasonic transducer (Aa) is quantified by one of a variety of transducers located onboard the device itself. In the case of mechanical application of the indentation load, Aa is quantified by a linear voltage displacement transducer or when applied by hand, remotely through a tracking device (optical, magnetic or inertial tracking). By obtaining data from ultrasonic waves reflected from a rigid, echogenic target (e.g. bone), the depth of the bone in relation to the position of the ultrasonic transducer may be determined. If this depth is quantified at the beginning and end of indentation loading, soft tissue compression (Ast) can be quantified by subtracting the depth of the bone found at maximal indentation from its depth at pre-indentation. The substitution of Aa and Ast values in the above equation results in the displacement of the rigid target in the plane of indentation (d).
The invention comprises both a method and apparatus. Accordingly, in one aspect of the invention, the invention comprises a diagnostic method of determining displacement of an osseous structure underlying soft tissue in response to an indenting force applied to the soft tissue and the osseous structure, comprising the steps of:
(a) providing an ultrasonic transducer/indenter having indenting surface;
(b) positioning the transducer/indenter over a target comprising the osseous structure underlying a layer of soft tissue;
(c) positioning the transducer/indenter in contact with the soft tissue, without substantially indenting the soft tissue;
(d) recording a first set of ultrasound data;
(e) moving the transducer towards the osseous structure while measuring the displacement of the transducer/indenter;
(f) recording a second set of ultrasound data;
(g) determining the soft tissue compression by comparing the first ultrasound data to the second ultrasound; and
(h) subtracting the soft tissue compression from the total displacement of the transducer/indenter to determine osseous displacement.
In another aspect of the invention, the invention may comprise an apparatus for diagnosing a disorder of a musculoskeletal system by determining displacement of an osseous structure underlying soft tissue in response to a load, said apparatus comprising:
(a) a support frame;
(b) an electromechanical actuator attached to the frame and having a thrust tube;
(c) control means associated with the actuator for controlling movement and direction of movement of the thrust tube;
(d) an ultrasonic transducer/indenter mounted to the thrust tube;
(e) a load cell mounted between the thrust tube and transducer/indenter;
(f) a linear position transducer associated with the actuator for determining the displacement of the thrust tube;
(g) first processing means for analysing ultrasound data taken by the ultrasonic transducer/indenter and determining soft tissue thickness and changes in soft tissue thickness; and
(h) second processing means operatively connected to the linear position transducer and to the first processing means for calculating osseous displacement from the displacement of the thrust tube and changes in soft tissue thickness.
In another aspect, the invention may comprise a system for diagnosing a disorder of a musculoskeletal system such as the spine by determining displacement of an osseous structure underlying soft tissue, in response to an indentation load, said apparatus comprising:
(a) a handheld ultrasonic transducer/indenter which produces and transmits ultrasonic derived data;
(b) a locator device associated with the transducer/indenter which communicates with a location sensor;
(c) means associated with the location sensor for determining the location of the transducer/indenter and for calculating the displacement of the transducer/indenter;
(d) a first processor adapted for receiving and analysing the ultrasound derived data and determining soft tissue thickness and changes in soft tissue thickness; and
(e) a second processor operatively connected to the first processor and the location determining means, said second processor adapted for calculating osseous displacement from the displacement of the transducer/indenter and changes in soft tissue thickness.
The processing means or processors referred to herein may include a general purpose computer programmed with appropriate software, or programmable firmware or a programmed logic controller or other hardware or software known to those skilled in the art.